Synthesis And Application Of Al Substituted-layered Double-hydroxide/Reduced Graphene Oxide Composites For Supercapacitor

Supercapacitors have attracted much attention as one of the energy storagesystems due to its high power density and good cycle life, which combines theadvantages of both dielectric capacitors that can deliver high power within a verysmall period and conventional rechargeable batteries that have high energy densities.Therefore, supercapacitors have a wide range of applications and have alreadybecome one of the research interests relative to new chemical energy sources. Themain researches about supercapacitor focus on the design and synthesis of electrodematerials. Transition metal oxides/hydroxides are attractive materials for electrodes ofsupercapacitors due to their high specific capacitance. More recently, there has been asignificant interest in exploring graphene as direct electrode materials or one ofcomponents in the composited electrode materials with its high performance due totheoretical surface areas of2630m2·g^-1，outstanding chemical stability, highelectrical， thermal conductivity, mechanical strength and flexibility forsupercapacitors. This dissertation is associated with the preparations of electrodematerials and the investigations of capacitive performances. The mains are as follows:1、The reduced graphene oxide/Al-Ni layered doubled-hydroxide with differentmass ratios were directly prepared using Ni（NO3）2and Al（NO3）3as the raw materialand urea as reductant and precipitant through hydrothermal method. The structure,chemical groups and morphology of the as-prepared composites were characterizedusing X-ray diffraction （XRD）, Fourier transform infrared spectrometer （FT-IR）,Raman spectrometer and field emission scanning electron microscopy （FESEM）,respectively. The electrochemical performances of the composites were investigatedby cyclic voltammetry, galvanostatic charge–discharge. The experimental resultsshowed that the composites with the mass ratio of LDH to rGO up to96.2:3.8exhibited optimal capacitive performance and reached the specific capacitances of918.4F·g^-1at the current density of1A·g^-1, which were much higher in comparisonwith pure Al-Ni layered doubled-hydroxide （LDH）(732F·g^-1).2、The layed Al-Co layered doubled-hydroxide/reduced graphene oxide withdifferent mass ratios was directly prepared using Co（NO3）2and Al（NO3）3as the rawmaterial and hexamethylenetetramine（HMT） as the source of OH-through mild reflux. The structure and morphology of the as-prepared composites were characterized usingX-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM）,respectively. The thermal stability of the sample was analyzed by thermogravimetry（TG）. The electrochemical performances of the composites were investigated bycyclic voltammetry, galvanostatic charge–discharge. The experimental results showedthat the composites with the mass ratio of LDH to rGO up to97.72:2.28exhibitedoptimal capacitive performance and reached the specific capacitances of937F·g^-1atthe current density of1A·g^-1, which increased by51.4%in comparison with pureAl-Co layered doubled-hydroxide （LDH）(618.8F·g^-1).3、The RuO2/rGO with different mass ratios were directly prepared using RuCl3and GO as the raw material through hydrothermal method. The structure andmorphology of the as-prepared composites were characterized using X-ray diffraction（XRD）, field emission scanning electron microscopy （FESEM）, respectively. Thethermal stability of the sample was analyzed by thermogravimetry （TG）. Theelectrochemical performances of the composites were investigated by cyclicvoltammetry, galvanostatic charge–discharge. The experimental results showed thatwhen the mass ratio of RuO2to rGO is equal to73.9:26.1, composites exhibited goodcapacitive performance and reached the specific capacitances of750F·g^-1at thecurrent density of1A·g^-1. Meanwhile, FESEM image of the composite was alsochanged when compared with the FESEM images of pure RuO2.